Update: 12:55 CDT TD9 has officially been upgraded to Tropical Storm Hermine. Because of Aircraft observation from hurricane hunter. Not because of satellite, ship, or drone observations.

Tropical Depression (TD) #9
The insurance industry needs to continue to focus on Tropical Depression (TD) #9 which has been trolling the industry for 14 days. It refuses to take the next step to become named storm “Hermine.” If I had a dollar for every time a model suggested a named storm would develop in the next 12 hours, I would be a wealth meteorologist.

This leads me to the next point: the National Hurricane Center (NHC) classification for storms that approach the U.S. coastline have become increasingly technical in recent years. It is bothersome because it has an impact on the insurance industry. Sandy is a recent example of how technical the NHC storm classification has become. Sandy was downgraded from a hurricane to a post-tropical cyclone less than 100 miles from the New Jersey coastline. With TD #9, countless observations many have suggested that TD #9 should have been a tropical storm. In fact, a ship just recently observed winds of 35 kts.

This bothers me because back in early 1900’s, storms were classified based on simpler information, such as ship observations. There were no drone aircraft or various other heavily scientific equipped aircraft flying into storms to examine the exact center of circulation. The historical catalogs that are used to create today’s catastrophe models have always used ship reports and flooding rain reports from newspapers to suggest a named storm was likely in the area. This was how storms were classified before all this great technology that allowed the NHC to become so technical. This additional technical information skews modern-day historical catalogs from how it would have otherwise been classified, and it could influence catastrophe models understanding of future named storm risks.

However, storm category is less relevant to the insurance industry at this point in time. The industry needs to focus in on impacts, regardless of what category is ultimately assigned to the system in the Gulf. Which is another lesson learned from Sandy, even a non-hurricane can have hurricane impacts. TD #9 will likely have impacts similar to hurricanes as it tracks northeast over the next several days and makes landfall Thursday night somewhere north of Tampa in the Big Bend region of Florida.

Florida Threats
The main threat at this time is heavy rainfall and flooding. Many parts of Florida will continue to experience heavy rain with a 3” – 13” swath of rain predicted across much of northwestern Florida. Flooding is expected in inland areas and coastal areas as well, as the Big Bend region of the coastline is prone to storm surge. The NHC now issues very detailed storm surge forecasts with every advisory.

Depending on the strength of TD #9 at landfall, winds may gust strongly enough to cause tree damage and power outages. An absence of recent hurricanes made the area ripe for tree falls. Soil moisture is already above normal for the projected landfall area, and even a weak gust of wind can down unhealthy or overgrown trees. A good natural cleaning of foliage can be expected.

Lastly, along with any tropical system there is always a risk of isolated tornadoes. The northern and central parts of Florida and far southern parts of Georgia are at risk as the center of the system moves across Florida later this week.

BMS clients can preview many of these hazards by using iVision to better understand their exposure to the upcoming event.

Post-Landfall Florida
Some models suggest that after the system makes landfall in Florida, it could hang around off the East Coast and maybe even make a second landfall in the Northeast later next week. But before we examine the storm’s next move, we need it to move to the Northeast from its current stationary location.

The next three weeks are traditionally the peak of the Northern Hemisphere tropical cyclone season. Mother Nature surely knows as there are now eight tropical systems to watch across the Northern Hemisphere:
• Five are being monitored for landfall over the next five days.
• Four threaten the U.S. coastline.
• Two have been classified as Hurricanes Madeline and Lester, and both are in the East Pacific tracking westward towards Hawaii. Madeline will closely approach the Big Island of Hawaii on Wednesday night, and if the track holds, Lester is forecasted to move past the Big Island on Saturday.Tropical Depression (TD) #8 is located 210 miles east the Outer Banks of North Carolina and will make close approach to Cape Hatteras, all before turning back out to sea tomorrow night. At this time, no insured loss is expected with this system as tropical-storm force winds are expected to remain just offshore.TD #9 is our old friend Invest 99L that, after much fanfare last week, took 11 days to develop into a tropical depression. This system still needs to be watched closely as it has the highest potential to impact the insurance industry. Although the upper air conditions (Strong Wind Shear) are not ideal for hurricane development, the sea surface temperatures are very warm off the west coast of Florida. TD #9 should be a named storm later today.
As a result of a cold front that will provide cooler weather over much of the East Coast for the long Labor Day weekend, this will also allow the system to turn to the northeast and lead to a track that will cross northern Florida with landfall in the Great Bend region on Thursday. Thereafter, the track calls for the system to accelerate out to sea off the coast of the south-eastern U.S. TD #9 is expected to continue slight strengthening as it curves northeast in the eastern Gulf of Mexico in the next 36-48 hours. It should be noted that this system has a history during which multiple models over-forecasted storm intensification. Now, based on the current intensity ratings issued by many of the forecast models, the NHC seems to have opted for a more conservative forecast. Below are the current NHC’s chances of winds reaching tropical-storm force in the next 5 days, which are 30% or less at individual locations in Florida.

The biggest impacts to the insurance industry would be tropical storm force winds, which could include minor damage and tree fall damage. Rainfall is expected to be 3” – 6” across much of Florida over the next five days so localized flooding is possible.

Lastly invest 92L is coming off of Africa and has a 40 – 50% chance of development over next 10 days and is expected to track toward the U.S. coastline similar to invest 99L over the last 11 days. Let’s hope the drama around invest 99L last week does not lead the insurance industry to disregard the next threat as we approach the peak of the season September 10th.

In the past six days the insurance industry has waited and watched for tropical wave Invest 99L to develop into a named storm. Frankly, it’s getting tiresome.

Six days ago at this time many models predicted Invest 99L would become a full named hurricane.

Above is the 00z run of the GFS model on August 19th valid for this coming Monday, August 29th, which had Invest 99L at a category 5 hurricane as it safely re-curves away from the East Coast.
It is all but certain this scenario will not play out, and once again, it reemphasizes the point that there can be large model errors that exists in hurricane forecasting. In fact, this reminds me of my February presentation at the Reinsurance Association of America Cat Modeling conference on HypOcane. This presentation examined the large forecasting errors associated with Erika and Joaquine in 2015. These errors led to unnecessary hype due to the over-reliance on numerical models. We can’t forget that forecasting tropical systems it not an exact science. The track errors are improving for named storm forecasting, but intensity forecasting still remains a challenge. Invest 99L highlights these challenges as some models suggested six days ago that there would be a tropical system nearing the Bahamas; however, the intensity guidance was all over the place as shown in the scenario above.

Last 9 ECMWF track forecasts for Invest 99L. The two Gulf coast landfalls were 8-day forecasts and were highly uncertain. This option is still on the table.

Last 26 GFS track forecasts for Invest 99L. All but two focused on Florida. The last few model runs of the GFS model have hard time tracking Invest 99L.

NOAA hurricane hunters continue to find a poorly organized tropical wave southeast of the Turks and Caicos Islands. There are times where tropical-storm force winds have been observed, but a lack of a well defined center of circulation with convection continues which is needed for named storm status. This could change at any time.
So for now, it is the same old story: there is a chance of a storm developing, and conditions west of the storm are ripe for development due to very warm sea surface temperatures, less dry air aloft and lower wind shear environment.

What we know today about Invest 99L:
• Models slow the forward speed of 99L late this weekend into early next week. This lessens the chance that the system will move into the western Gulf of Mexico, and increase the chances the system will move into eastern Gulf of Mexico.
• If a named storm develops, Louisiana/Mississippi/Alabama landfall cannot be ruled out, but models suggest Florida is at peak risk. Time is however running out as the system tracks closer to Florida.
• Most models provided poor intensity guidance. If the system is ultimately named, hurricane development can not be ruled out due to the warm sea surface environment in the forecasted path of the system.

It’s time for U.S. insurers to take careful note of tropical wave 99L that I blogged about on Friday. This tropical wave is currently 400 miles to the east-southeast of the Leeward Islands. At its current translation speed of 15-20 mph, the wave will reach the eastern Caribbean tomorrow morning and Puerto Rico on Thursday. A hurricane hunter is slated to investigate 99L this morning, and the data it collects could suggest a high likelihood that the tropical wave will develop into a named storm: the name “Hermine” awaits. This hurricane hunter data will also provide improved data for numerical weather models and will augment future track forecasts.

Future Possible Track
Climatology suggests Invest 99L is at least six days away from any U.S. interaction, so a great deal of uncertainty still exists within the forecast. However, based on its current location, climatology suggests with 32% probability that a named storm will impact the U.S. and with 27% probability that a named storm will make U.S. landfall.
When you factor in forecast-model suggestions, these probabilities increase: model consensus indicates that Invest 99L will track toward the Northern Caribbean islands. Some divergence starts to occur at this point within the models: Some of the models take the system into south Florida and some take the system into the Bahamas. But either scenario increases the probability that the system will track toward the U.S. over the next few days.

Despite forecast uncertainty, many scenarios have potential to play out in the next six days. One historical marker looms large. On this date in 2005, Tropical Depression 12 formed in the Bahamas and was forecasted to track toward Florida as a tropical storm. A few days later, Tropical Depression 12 developed into Katrina and hit south Florida. It was the last August hurricane to make landfall in Florida. We now know Katrina quickly gained strength in the Gulf of Mexico to become one of the most devastating hurricanes in U.S. history. It should also be noted 24 years go today hurricane Andrew made landfall in south Florida after rapidly strengthening near the Bahamas. Just as was experienced with hurricane JOAQUIN storms can rapidly strengthen in this general area given the very warm sea surface temperatures.

TD 12 forecast on this date in 2005. TD 12 went on to be hurricane Katrina.

Katrina, Andrew, Joaquin serve as a reminder that hurricanes can develop rapidly in the right conditions and forecast tracks have uncertainty five to six days out. In the more than 10 years since Katrina, weather models have improved, and they suggest tropical troubles could be brewing closer to the U.S. later this weekend. These 11 years since Katrina have also brought new and untested insurance companies and 2 million additional Florida residents, many of whom have never experienced a hurricane. All of these facts add up to the conclusion that Invest 99L requires careful watch over the next several days.

Other Systems:

Fiona – continues to weaken south of Bermuda and is no longer being watched by the National Hurricane Center. It maybe come back to life so stay tuned, but stay out to sea.

Gaston – should become a hurricane later today and track into the central Atlantic and east of Bermuda early next week.

This week the sixth named storm (Fiona) of the Atlantic hurricane season formed from a fairly strong African wave. However, as it tracks slowly west, Fiona is fighting high wind shear and the SAL, and as a result, it continues to be a weak tropical storm located about 1,295 miles west of the Cape Verde Islands. Fiona should continue to track to the northwest over the weekend and will likely stall early next week as a weak tropical depression near Bermuda – if it even makes it that far. So at this time, Fiona does not appear to threaten the insurance industry.

Invest 99L
Unlike Fiona, Invest 99L may be the bigger threat to the insurance industry. Invest 99L is an area of disturbed weather currently labeled by the National Hurricane Center (NHC), and to understand Invest 99L, a football analogy may help. Fiona functions as a lead blocker. She sealed off the SAL, allowing Invest 99L to go wide left into more fertile territory later this weekend: as described in my earlier posts, as tropical systems move closer to the U.S., they are likely to develop and strengthen. Likewise, Invest 99L may intensify as it tracks westward to this more fertile territory.

Invest 99 is worth mentioning because the NHC currently indicated a 50% chance that it will develop into named storm Gaston. They project this system will track into the Leeward Islands over the next five days, and as this storm tracks west, it will encounter increasingly warm sea surface temperatures.

Invest 99L is currently favored by models to develop and strengthen in the coming days. However, as stated, this is also the season when the media tend to highlight a single model run as a doom-and-gloom scenario.

Often this far in advance, these forecasts don’t verify, and all forecast scenarios need to be considered at this time. There are a multitude of scenarios still in the playbook for Invest 99L after all it’s not even a named storm yet.
Below is a look at the U.S. Global Forecast Model (GFS) ensemble model output. In total, this is a model run with 21 different forecasts to create an ensemble. The current forecast run demonstrates the uncertainty in the forecast in terms of track.

Below is a summary of various forecast model intensity guidance as Invest 99L tracks westward over the next five days.

In summary, Invest 99L has a high chance of developing into tropical storm Gaston over the weekend. There is some uncertainty in its long-range forecast track, but we know with high confidence that the system is expected to track toward the western Caribbean where the water is warm enough to support healthy hurricane development. If atmospheric conditions are ideal next week, a potential hurricane could approach insurable risk in the Caribbean and U.S. If these conditions late next week are not ideal, the current tropical wave could be just that – a tropical wave.